MUTATION OF GLYCINE-185 TO VALINE ALTERS THE ATPASE FUNCTION OF THE HUMAN P-GLYCOPROTEIN EXPRESSED IN SF9 CELLS

A single amino acid substitution, Gly(185) --> Val, in the human P-gly coprotein (Pgp) was previously shown to cause an altered pattern of dr ug resistance in cell lines transfected with the MDR1 cDNA carrying th is mutation, To further define the function of amino acid 185 in the P gp, the wild-type and the mutant Val(185) Pgps were expressed in Sf9 i nsect cells, and their biochemical properties were compared, Verapamil - and colchicine-stimulated ATPase activities were markedly increased with concomitant increase in affinity for these compounds with Gly(185 ) --> Val substitution in the Pgp, However, the vinblastine-stimulated ATPase activities of the wild type and Val(185) Pgps were nearly iden tical. Because transport substrate-induced ATP hydrolysis is generally thought to reflect transport function, these data suggest that colchi cine and verapamil are transported at an increased rate with Gly(185) --> Val substitution in the Pgp. These results also indicate that amin o acid 185 is involved in verapamil and colchicine, but not in vinblas tine, binding/transport. Kinetic analyses indi cate that cyclosporin A , an inhibitor of Pgp, binds to the verapamil and vinblastine binding/ transport site(s) in the Pgp, Taken together, the results presented he rein reveal that the verapamil and vinblastine binding/transport site( s) are in close proximity and that the cyclosporin A binding site span s the common region of these two drug binding/transport site(s) in the Pgp molecule.